asp.net core 3.1 - Worker Service Template - SignalR Implementation

I am trying to broadcast a message to clients with a worker service in .net core 3.1. I don't have any Startup.cs (no endpoint etc.). I only have a Program.cs:

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
        .UseWindowsService()
            .ConfigureServices((hostContext, services) =>
            {
                //services.AddSignalR();
                services.AddHostedService<Worker>();
            });
}

And this is the worker (Worker.cs):

public class Worker : BackgroundService
{
    private readonly ILogger<Worker> _logger;
    //private readonly IHubContext<OperatorHub, IMessage> _operatorHub;



    public Worker(ILogger<Worker> logger/*, IHubContext<OperatorHub, IMessage> operatorHub*/)
    {
        _logger = logger;
        //_operatorHub = operatorHub;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            //await _operatorHub.Clients.All.SendMessage("hello fucking world!");
            _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
            await Task.Delay(1000, stoppingToken);
        }
    }
}

From what I gathered from seperate documentation (but right there is no documentation on internet about this) This is an Interface I created (IMessage.cs):

public interface IMessage
{
    Task SendMessage(string message);
}

And this is a hub class (OperatorHub.cs):

public class OperatorHub : Hub<IMessage>
{
    public async Task BroadcastMessage(string message)
    {
        await Clients.All.SendMessage(message);
    }
}

When I run I get an exception because of the line services.AddSignalR(); in Program.cs. I tried to add something like services.AddSingleton<OperatorHub>() under ConfigureServices but no luck either.

A little help would be much appreciated. Thanks in advance.